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The ubiquitin–proteasome system is involved in the regulation of activity of spermadhesin aqn1 and acrosin inhibitor, the two sperm surface proteins, during porcine fertilization
Jonáková, Věra ; Yi, Y.J. ; Postlerová, Pavla ; Pěknicová, Jana
The spermadhesin AQN1and acrosin inhibitor (AI/SPINK2) proteins bind to the sperm plasma membrane at ejaculation. The AQN1 has been implicated in sperm binding to zona pellucida (ZP) of the oocyte as well as in sperm interactions with the epithelium of the oviductal sperm reservoir. The SPINK2 protects spermatozoa from proteolytic degradation during their trip up the female genital tract toward the oocyte. This study examined the role of two components of the 19S proteasome regulatory complex, the ubiquitin C-terminal hydrolase UCHL3 and PSMD8 in the AQN1-mediated boar sperm binding to zona pellucida. Interaction of PSMD4 subunit with the acrosomal surface-associated acrosin inhibitor AI/SPINK2 provided another line of evidence for the presence of 26S proteasomes on the sperm surface. Detection of the ubiquitinated forms of SPINK2 supports the hypothesis that SPINK2 activity is controlled by ubiquitin-proteasome system (UPS). The activity of the porcine AQN1, and thus the efficiency of sperm-oocyte recognition/binding, may be controlled by elements of the sperm surface-bound UPS, in particular by UCHL3, and by proteasomal regulatory complex subunit PSMD8. Ubiquitinated isoforms of AQN1 were also detected in boar sperm extracts. The UCHL inhibitor ubiquitin aldehyde and the antibodies against UCHL3 or PSMD8 increased the rate of sperm-ZP penetration and polyspermy during porcine in vitro fertilization (IVF). In contrast, the addition of recombinant UCHL3 to fertilization medium significantly reduced polyspermy rates, while maintaining satisfactory rate of monospermic fertilization (~50%). These results are significant for production agriculture. The high level of polyspermy that hinders porcine IVF for commercial embryo transfer could be mitigated by the modulation of the UCHL3 and/or PSMD8 activity.

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